Hydronic radiant panel heating is a popular form of heating for habitable structures. This form of heating typically incorporates tubing carrying a heated fluid, that transfers heat from the tubing to a panel, which then conducts that heat across the surface of the panel, thereby transferring heat to the habitable space within the structure. These panels are most commonly a part of a floor assembly but can also be a part of wall or ceiling assemblies.
Historically, radiant panels were largely comprised of circuits of tubing forming continuous serpentine or spiraling loops embedded in a slab comprised of Portland cement concrete or gypsum based concrete. Recent developments in hydronic radiant heating have focused on arrays of modular panels that rely on aluminum or other conductive materials to distribute heat from the tubing across the surface. Some systems have been manufactured with the tubing already permanently secured within the panel. In these instances, while the tubing may be securely contained within each panel, numerous connections must be made between individual panels within an array in order to complete a circuit through which the heated fluid may be circulated. The inherent challenge in these systems is that each connection adds to the labor at time of installation, and the likelihood of leaks multiplies with the number of connections, each of which must be accomplished without defect and maintain their integrity for the lifetime of the structure.
Systems seek to avoid this challenge by installing the tubing after the panel array is installed in the structure. This allows the tubing to be continuous, with the exception being the connections at the beginning and end of each loop, but without connections between individual panels, thereby reducing labor and the likelihood of leaks. In most of these continuous loop systems, the tubing is retained in a modular system of channels designed to receive and securely retain the tubing in contact with the conductive material of the panel. The conductive function of the panel is enhanced when the contact area of the tubing with the conductive panel is maximized.
Various forms of polymer tubing are used in these systems with a common being cross-linked polyethylene often known as PEX tubing. It is in the nature of PEX, and other polymer tubing typically used, that there is memory in the tubing. Memory is the property of polymers that causes them to tend to return to their original molded shape after being deflected to from that shape. Memory causes the tubing when deflected to act like a spring. Memory tends to resist both twisting and bending. Accordingly, due to the spring-like nature, without positive means for retaining the tubing in the channels, it may become dislodged from the channels. Virtually all of these systems incorporate features in their systems to keep the tubing firmly in place. The means for retaining the tubing in channels in some systems is a mechanical feature that causes a narrowing and therefore a restriction at the top of the channel causing the tubing once pressed past the restriction, to be restrained from returning back pass the restriction and out of the channel. To do so limits the efficiency of forming the channel thereby driving up the cost of manufacturing. Other panel systems use adhesives. While adhesives work, they can add cost, can be messy, and even when used, the tubing may need to be temporarily restrained in the groove, until the adhesive achieves a proper cured strength, adding further cost. Some systems rely on an interference fit between the tube and the channel by slightly under-sizing the channel relative to the tubing size so as to create friction with the tubing, see U.S. Pat. No. 5,788,152 to Alsberg which is incorporated by reference in its entirety herein. The problem with this approach is that radiant heating panel systems tend to have a channel pattern, which requires the tubing to be straight in some areas of the panel and turn through an arc at other areas. When any tubing is bent into an arc, the bending forces tend to deform the tubing cross section from its normal round profile to a more oval shape, which tends to make the tubing narrower relative to the width of the channel where bent and therefore have less of an interference fit or even none. Those systems that have relied on the interference fit have found that the tubing is not well retained at curved portions of the channels and have used either adhesives, mechanical fastenings or both to overcome this challenge. These approaches to a solution have caused increased labor and material costs. In some cases, use of tubing with a deformable layer within the wall of the tubing has been employed. Three-layered PEX-Aluminum-PEX is a common form of this tubing used. Due to the malleability of the aluminum, this type of tubing may be better retained than pure polymer tubing. But such tubing is nearly twice or more of the price of simple one layer polymer tubing. Even with the deformable layer, retention in the channel may still be compromised.